Aldehydes have been used for many years in the medical sciences for various purposes. It is well known, for example, that formaldehyde and glutaraldehyde are useful for fixing and preserving tissue specimens. In recent years, the role of aldehydes in the medical community has expanded to that of a germicide useful for disinfecting or sterilizing medical instruments.
Glutaraldehyde is a commonly used dialdehyde in the medical industry. Typically, glutaraldehyde is used as a germicide for disinfection of reusable medical devices, such as surgical instruments or endoscopes. The effective level of glutaraldehyde in commercial disinfection solutions generally ranges from about 1.5% to 3.5%, by weight of the solution. For example, CIDEX® 14 Day solution contains 2.4% glutaraldehyde as the active ingredient, and CIDEX® 28 Day solution contains 3.5% glutaraldehyde as the active ingredient.
The effectiveness of the germicidal solution is related to the concentration of the aldehyde. The monitoring of the aldehyde levels in the germicide solution is particularly important in assuring the effectiveness of the disinfectant. Unfortunately, presently available aldehyde assay procedures generally either lack accurate quantification or involve complicated sample preparation, which reduces the convenience and efficiency of the assay.
For example, U.S. Pat. Nos. 4,521,376 and 4,643,980 disclose a test system for glutaraldehyde consisting of a mixture having a defined ratio of sodium sulfite and an amine compound, in particular the amino acid glycine. The sodium sulfite and the amino acid react with glutaraldehyde to form a yellow-colored complex. In practice, the commercial product utilizing the principles described in U.S. Pat. Nos. 4,521,376 and 4,643,980 involves a three-step reaction. First, glutaraldehyde is reacted with sodium sulfite to form a sulfite addition product and sodium hydroxide. Second, sodium hydroxide reacts with glycine to form sodium glycinate. Third, sodium glycinate reacts with another molecule of glutaraldehyde to form a yellow-colored addition product. The test strips based on this chemical sequence are “semi-quantitative” chemical indicators for use in determining whether the concentration of glutaraldehyde is above or below an established minimum concentration for a solution. The test strips are commercially available as the CIDEX® family of solutions test strips (Johnson & Johnson Medical, Inc., Arlington, Tex., U.S.A.).
The “semi-quantitative” test strip is a qualitative threshold test to determine whether the concentration of glutaraldehyde in a given sample meets a designated threshold. The test serves to indicate, either positively or negatively, whether the disinfectant solution contains a required minimum effective level of glutaraldehyde. A sample that contains the threshold level changes the color of the strip to yellow, indicating that the sample passes the assay. If the sample does not contain the threshold level of glutaraldehyde, the strip does not undergo a color transition, indicating that the sample fails the assay. The test does not provide a continuous quantitative assay of glutaraldehyde levels in the solution.
Moreover, the reaction described in U.S. Pat. Nos. 4,521,376 and 4,643,980 requires the use of both the sulfite and the amine compound to afford the desired color response. Neither patent discloses that an amino acid alone can form a chromophore, permitting quantification of an amount of aldehyde, particularly glutaraldehyde. In addition, neither patent discloses use of a diamino carboxylic acid in any assay, either quantitative or qualtitative, for aldehydes, including dialdehydes.
Sodium sulfite and bisulfite methods as well as reactions with organic nitrogen containing compounds have been described for quantitative assay of aldehydes, but typically formaldehyde. These methods are tedious, and require a multistep titration to afford an accurate result. In addition, these reactions can generate strong base, such as sodium hydroxide, in sulfite/bisulfite methods, or, in the case of nitrogen containing compounds, the compounds, for example amino acids, can react as strong acids. The accurate quantitation of the strong acidic or basic component of the reaction is neither convenient nor feasible for a dry reagent test strip. A more thorough description of the sodium sulfite and sodium bisulfite methods can be found in J. F. Walker, “Quantitative Analysis of Formaldehyde,” in Formaldehyde, 3rd ed., Reinhold Publishing Corporation, New York, N.Y., pp. 486–488 (1964). Further description of the reaction of formaldehyde with organic nitrogen containing compounds, and more particularly amino acids, can be found in J. F. Walker, “Reaction with Amines, Amides and Nitriles,” in Formaldehyde, 3rd ed., Reinhold Publishing Corporation, New York, N.Y., pp. 359–414, in particular pp. 395–398 (1964).
Other assays typically employed for detecting glutaraldehyde use chromogenic reactions to form a colored adduct, such as described in U.S. Pat. No. 5,464,775. These reactions generally are used in a solution format assay for detecting glutaraldehyde in adult urine samples as evidence of urine adulteration. The assays require a chromogenic reaction of the aldehyde in a test sample with an aqueous carbonyl indicator, typically an aromatic azine or azide. These compounds are capable of forming a detectable chromogenic adduct. Examples of such indicator reagents named in U.S. Pat. No. 5,464,775 include, for example, 2,4-dinitrophenyl hydrazine, 4-nitrophenyl hydrazine, hydrazine, phenylhydrazine, semicarbazide hydrochloride, and hydroxylamine. Generally, these compounds have conjugated or aromatic systems that allow for color formation.
To date, no known single assay is available to quantitatively assay aldehyde concentrations based on the formation of a colored chromophore in an efficient, effective manner. Accordingly, it would be beneficial to provide an assay to analyze a test sample for aldehyde concentration, particularly glutaraldehyde concentration, in a simple, convenient dry test strip or solution format for detecting liquid or gaseous aldehyde concentration.